1. Field of the Invention
The present invention relates to a method according to the preamble of the appended claim 1 for setting up a connection state in a packet network, to a system according to the preamble of the appended claim 11, and to a wireless communication device according to the preamble of the appended claim 23.
2. Brief Description of Earlier Developments
Data transmission between different devices can be established in such a way that those communication devices between which data is to be transmitted at a given time, are connected for a time required in the data transmission. Thus, this so-called circuit-switched connection is effective until the user terminates the data transmission. In such cases, most of the communication time is passed feeding the commands given by the user and only a small share of the time is used for the actual data transmission. This restricts, for instance, the maximum number of simultaneous users of the same application. Another alternative is to utilize so-called packet switched data transmission. Thus, data is transmitted between communication devices in a packet format, wherein the time between packets is free to be used by other communication devices. Thus, the number of simultaneous users can be increased, especially in wireless data transmission networks, such as cellular networks, because then the wireless communication devices in the area of the same cell can use the same transmission channel. One cellular system is the GSM system (Global System for Mobile Communication), for which a packet format data transmission service GPRS (General Packet Radio Service) is developed. FIG. 1 presents in a block diagram the blocks essential for the operation of the GPRS system. A packet switching controller SGSN (Serving GPRS Support Node) controls the operation of the packet switching service on the cellular network side. The packet switching controller SGSN attends to the logging in and out of a wireless communication device MS, updating the location of the wireless communication device MS, and directing the data packets to right addresses. The wireless communication device MS is connected to a base station subsystem BSS via a radio interface Um (FIG. 1). The base station subsystem is connected to the packet switching controller SGSN through a BSS-SGSN interface Gb. In the base station subsystem BSS, a base station BTS and a base station controller BSC are connected with each other with a BTS-BSC interface Abis. The packet switching controllers SGSN can communicate with other packet switching controllers SGSN by means of a gateway GPRS support node (GGSN). The GPRS system is described, for example, in the draft proposals GSM 01.60, GSM 02.60, GSM 03.60 and GSM 04.60.
It is possible to divide the operation of both the wireless communication device MS and the packet switching controller SGSN into several layers, each having a different function, as presented in FIG. 2. The International Standardisation Organisation ISO has developed an OSI model (Open Systems Interconnection) for grouping data transmission into different functional layers. This model contains seven layers which are not necessarily needed in all telecommunication systems. The layers are, listed from top to bottom: an application layer, a presentation layer, a session layer, a transport layer, a network layer, a data link layer, and a physical layer.
The transmission of the information to be transferred, such as control signalling and data transmitted by the user, between the wireless communication device MS and the packet switching controller SGSN is advantageously performed in the form of data frames. The data frame of each layer consists of a header field and a data field. FIG. 2 also presents the structure of the data frames used in the GPRS system in different layers.
The information contained in the data field can be, for example, information entered by the user of the wireless communication device, or signalling data. In the following, the functions of the layers of the GPRS system will be presented.
In the data link layer the lowermost layer is a MAC layer (Media Access Control), which attends to using the radio channel in communication between the wireless communication device MS and the base station subsystem BSS, e.g. reserving channels in the transmission and reception of packets.
The data transmission between the base station subsystem BSS and the packet switching controller SGSN in the lowermost layer is conducted in the L2 layer (data link layer), using a data link layer protocol, such as the LAPD protocol according to the standard Q.921, a frame relay protocol, or the like. The L2 layer can also contain quality and routing data according to GPRS definitions. The L2 layer contains features of the physical layer and the data link layer of the OSI model.
Above the MAC layer, there is a RLC layer (Radio Link Control) for the purpose of dividing the data frames established by the LLC layer into packets of fixed size, transmissible on the radio channel (PDU, Protocol Data Unit), and transmitting and retransmitting them if necessary. The length of the packets in the GPRS system is the length of one GSM time slot (c. 0.577 ms).
The LLC layer (Logical Link Control) provides a reliable data transmission link between the wireless communication device MS and the packet switching controller SGSN. The LLC layer, for example, adds debugging data to the message to be transmitted, whereby it is possible to aim to correct incorrectly received messages and, if necessary, the message can be retransmitted. In addition, data encryption and decryption is conducted in the LLC layer.
Protocol modifications, compression, and segmentation of the data to be transmitted, and segmentation of the messages transmitted from an upper layer are performed in a SNDCP layer (Sub-Network Dependent Convergence Protocol). The structure of the SNDCP layer is also presented in FIG. 2. The SNDCP frame comprises a SNDCP header field and a SNDCP data field. The SNDCP header field consists of protocol data (Network Service Access Point Identity, NSAPI) and SNDCP control data, such as compression, segmentation and encoding definitions. The SNDCP layer functions as a protocol adapter between the protocols used in the upper layer and the protocol of the LLC layer (data link layer).
The information to be transmitted enters the SNDCP layer from an application advantageously in data packets according to a protocol (PDP, Packet Data Protocol), such as messages according to the X.25 protocol or packets of the Internet protocol (IP). The application can be, for example, a data application of a wireless communication device, a telecopier application, a computer program which communicates with a wireless communication device, etc.
The MAC layer, the RLC layer, the LLC layer, and the L2 layer contain features which are described in layer 2 in the OSI model. The aforementioned layers and the layers described in the OSI model are not, however, distinctly consistent.
The SNDCP frame is transferred to the LLC layer, in which an LLC header field is added to the frame. The LLC header field consists, for instance, of an LLC control element which defines the number of the frame and the type of the command (info, acknowledgement, request for retransmission, etc.). In connection with the login to the GPRS packet network, the wireless communication device sends an inlog request message to the packet switching controller SGSN. The packet switching controller SGSN can, on the basis of a wireless communication device identification IMSI (International Mobile Station Identity) retrieve information from the home location register HLR corresponding to the wireless communication device in question, wherein the packet switching controller SGSN can, on the basis of this data, select a temporary logical link identity TLLI for the data transmission connection. If the wireless communication device has previously had a TLLI identification in its use, the wireless communication device transmits this in the request message, wherein the packet switching controller SGSN can place this identification again at the disposal of the wireless communication device, or allocate a new TLLI identification. The packet switching controller SGSN transmits the selected TLLI identification to the wireless communication device to be used in the data transmission between the wireless communication device and the packet switching controller SGSN. This TLLI identification is used in the data transmission to define which data transmission connection the message in question belongs to. The same TLLI identification is allowed to be used in only one data transmission connection at a time. After the connection is terminated, the TLLI identification used in the connection can be allocated to a new connection which is being set up. This is described in more detail in the GSM standard 03.60.
The cells included in the packet network are divided by the operator of the packet network into routing areas, which can be used to define the location of the wireless communication device MS. Each routing area comprises one or more cells. Thus, with a mobility management function of the wireless communication device, the aim is to maintain information on the location and connection state of the wireless communication devices in the operating range of the packet network. This information is maintained both in the wireless communication device and in the packet network, advantageously in the GPRS support node SGSN. In the GSM system, the base station connected to the wireless communication device MS is changed when the cell is changed. In CDMA based (Code Division Multiple Access) cellular networks, the wireless communication device MS can be communicated simultaneously via several base stations. The base stations transmit a spread spectrum signal on a so-called pilot channel, wherein the wireless communication device can, on the basis of these pilot signals, conclude which base station has the most advantageous signal with respect to communication. Those base stations which are communicating with the wireless communication device MS at a given time, compose a so-called active set. The movement of the wireless communication device by means of the packet network of the CDMA system can be concluded from the alteration of these active sets.
In the GPRS system currently in use, the wireless communication device can have three different connection states in respect of the packet network: an idle state, a standby state and a ready state. In the idle state, the wireless communication device is not connected to the mobility management of the network, and communication is not possible. In the ready state, the wireless communication device is connected to the mobility management of the packet network, the location of the wireless communication device is known by the packet network with an accuracy of one cell, and the wireless communication device can both transmit and receive data packets. In the standby state, the wireless communication device is connected to the mobility management of the packet network, wherein the wireless communication device cannot either transmit or receive data packets, and the location of the wireless communication device is known by the packet network with an accuracy of the routing area only. The transition from the ready state to the standby state can be conducted, for instance, when a sufficiently long time has passed since the latest data packet was transmitted between the wireless communication device and the packet network. This time is measured advantageously with a ready counter.
When the wireless communication device is moved, its location and status is updated with signalling messages transmitted in the packet network. The wireless communication device is not, however, always in motion, but is, for example, in an office during a working day. Thus, the updating signalling for the location of the wireless communication device exerts an unnecessary load on the packet network and increases the power consumption of the wireless communication device. In addition, the transition from the standby state to the ready state requires paging signalling before packets can be transmitted between the wireless communication device and the packet network, which delays data transmission.
One purpose of the present invention is to provide a method for setting up a connection state in the packet network, a system applying the method and a wireless communication device which can be used in it. The present invention is characterized in what will be presented in the characterizing part of the appended claim 1. The system according to the present invention is characterized in what will be presented in the characterizing part of the appended claim 11. The wireless communication device according to the present invention is further characterized in what will be presented in the characterizing part of the appended claim 23. The invention is based on the idea that the packet network is supplemented with a connection state, an extended ready state, in which it is possible to set the wireless communication device connected to the packet network, especially when its location remains substantially unaltered and when the wireless communication device has no data packets to transmit or receive.
Considerable advantages are achieved with the present invention compared with methods, packet networks and wireless communication devices of prior art. With the extended active state according to the invention, loading of the packet network can be decreased, because the need for signalling is reduced when the wireless communication device is immobile. The reduced need for signalling also reduces the power consumption of the wireless communication device, thereby extending the standby time of the wireless communication device with one charging. In addition, data transmission is accelerated in situations when there has been a pause in the transmission of data packets, after which a new transmission is begun.